Intertidal crab prey pulse export quantifies the importance of tidal wetland connectivity

Abstract

A key value of saltmarshes is their role in providing trophic subsidies, notably in the form of prey pulses of crab zoeae (CZ). No studies to date, however, have investigated quantitatively the patterns between crab zoeae pulses and saltmarsh tidal connectivity in tropical estuaries. In this study, CZ densities were examined over successive tides and months using a zooplankton sampling pump to examine links between tidal fluctuations and pulses of CZ in a tropical Australian estuary with a complex of tidal saltmarshes, mangroves, and unvegetated flats. CZ densities were linked to spatially explicit information on tidal wetland inundation that was derived from Unattended-Aerial-Vehicle (UAV) Structure from motion (SfM) photogrammetry and two-dimensional hydrodynamic modelling. The study found that: (1) tidal connectivity is a key trigger to prey pulse export; (2) while tidal connectivity was critical in the export of CZ, not all tidal connections resulted in meaningful ecological connectivity; and (3) succulent saltmarsh was one of the tidal wetland types contributing to the export of CZ. Surprisingly, we reveal that not all succulent saltmarshes were uniformly participating in CZ export. These findings highlight the significance of quantitative eco-hydrological approaches to assess saltmarsh and tidal connectivity values. This study supports the need for management and restoration approaches to integrate a contextual understanding of the synergies between hydrology, ecology, and habitat heterogeneity. These data emphasise the need to move beyond generalisations that “similar” habitat type share similar ecological functions and should be managed equally.